1) Field of the Invention
The present invention relates to a high loft having balanced properties and a method of making the same for the production of nonwoven fabric. In particular, the present invention relates to a lightweight, high loft nonwoven fabric in which properties in the machine direction and cross direction such as resiliency (measured in terms of improved loft), and improved tensile strength are more uniform. Additionally, a process for making the high loft nonwoven is unique in that a drafter machine is employed, thereby increasing the efficiency of the production process.
2) Prior Art
High loft nonwoven fabrics are used in a wide variety of applications, for example, in indoor and outdoor furniture, bedding such as mattresses, and quilting. As such, there is always a need to improve the quality of nonwoven fabrics to enhance their function with existing uses, and to add their application to new uses. Moreover, from an economics standpoint, it is desirous to improve the process of producing nonwoven fabric in order to increase production rate.
High loft, nonwoven fabrics are principally formed of a polyester blend having a low melt binder. The low melt binder is either a bicomponent fiber, or a low melting fiber having a lower melting temperature than the polyester fiber, or a latex resin applied to the fibers, either as a spray or a powder.
Two principle characteristics of high loft nonwoven fabrics are product resiliency and tensile strength. Product resiliency refers to the capability of the fabric to return to its original shape after having been compressed. For example, it is desirable that a cushion, mattress, or similar item returns to its original form after use, such as after being sat upon by a person. Also, during shipping, the product is usually vacuumed down to reduce shipping volume. As such, it is important that the product returns to its original state upon unpacking.
Tensile strength refers to the capacity of the fabric to resist a load applied in tension and is measured in the machine and cross directions. Machine direction refers to the direction in which the nonwoven material is manufactured and processed, and cross direction is transverse to the machine direction.
Other important measures of quality include product uniformity, product compression recovery, and the amount of false loft exhibited by the product. Product uniformity refers to the degree of fiber alignment in both the machine and cross directions, such that the product possesses more uniform physical properties. Compression recovery and false loft are related to resiliency in that they affect fabric's ability to return to its original shape. For example, a fabric with false loft will have a high initial loft due to excessive voids within the fabric. Upon removal of an applied load, the fabric will be compressed into the voids and will not return to its original form.
In a conventional process for making high loft nonwoven fabric, wherein low melt fibers are used as the binder, polyester fibers and low melt fibers are blended together in a hopper, for example, and deposited onto a moving conveyor belt forming a batt. The speed of the conveyor belt determines the thickness of the batt. Movement of the conveyor belt naturally orients the majority of the fibers in the machine direction. However if higher tensile strengths are desired, more orientation in the machine direction will provide this effect. For example, the fibers may be carded to align the fibers more uniformly in the machine direction to give higher tensile strengths. To provide tensile strength in the cross direction a cross lapper layers the fibers over the machine direction laid fibers to thicken and strengthen the web. The web is then passed through an oven having sufficient heat to melt the low melt fibers, causing them to bind to the other fibers, thereby strengthening and improving resiliency of the web. After leaving the oven, the properties of the web are set in a cooling zone and the batt is wound for shipping to customers. This is the conventional process for producing the highest quality high loft product.
This conventional process is limited in that tensile strength of the web in the cross direction is higher than the tensile strength in the machine direction. Another drawback of the conventional process is that the low melt fibers typically constitute twenty percent (20%) or more of the web, by weight. These low melt fibers are more expensive than the polyester fibers, adding cost to the product.
A further limitation of the conventional process is that the production rate is limited by the cross-lapper. That is, the faster the production rate, the more inconsistent the fibers are laid when cross lapped. Moreover, the cross lapper is incapable of cycling back and forth at a speed sufficient to keep up with the speed of the other production components. This is particularly a problem for lightweight, nonwoven fabrics wherein inconsistently laid fibers reduce the fabrics' quality and diminishes physical properties of the product.
An alternative to using a low melt fiber as a binder in a conventional process for producing high loft nonwoven fabrics is to spray a latex resin onto the polyester fibers. The latex resin is applied in a spraying area sequentially located between the cross lapper and oven. Disadvantageously, the step of applying resin is also quite slow in comparison to the process speed of the remaining equipment, causing another process restriction point. Moreover, the latex resin causes the fabric to have a stiff feel.
It is the object of the present invention to provide a process for producing high loft nonwoven fabric at a faster production rate than conventionally accomplished. It is also an object of this invention to provide a product and process for producing high loft nonwoven fabric having comparable and in most cases superior quality, particularly having uniformity in tensile strength in the machine and cross directions. Further, it is an object of this invention to provide a product for making high loft nonwoven fabric that has improved product uniformity, enhanced compression recovery, and a reduction in false loft. Still further, it is an object of this invention to provide a product and process that produces a high loft nonwoven fabric, containing a reduced amount of low melt fibers, that is comparable or superior to fabric produced by a conventional process.
The present invention achieves these objectives in producing nonwoven fabric by adding a drafter within an existing high loft nonwoven process, between the cross lapper and oven. The drafter functions in its conventional sense, but its use in producing high loft nonwoven fabric is novel, thus producing novel products, and the benefits to product quality and increased production rate resulting therefrom was unexpected.
Drafters are known to those skilled in the textile art for producing thin fabrics. Drafters are typically used in processes which include needle punching, wherein the needle punching strengthens the web. However, their use in producing lightweight, high loft nonwoven fabric, is not known.
Applicant is aware of the following U.S. patents concerning a process having a drafter for producing nonwoven fabric.
U.S. Pat. No. 5,475,903, issued to Collins on Dec. 19, 1995, describes a hydroentangled, nonwoven fabric having comparable strength in the machine and cross directions. The process includes carding, cross lapping, drafting and hydroentaglement to create a thin fabric suitable for use in hospital gowns. The hydro entanglement step imparts comparable strengths to the fabric in the machine and cross directions. Since the process relates to manufacturing a thin fabric, there is no consideration of product resiliency.
U.S. Pat. No. 5,252,386, issued to Hughes et al. on Oct. 12, 1993, describes a process for making an entangled nonwoven fabric having balanced strength properties in the machine and cross directions and improved fire retardancy. These characteristics are achieved by cross-stretching the entangled fabric after the fabric has been wetted with an aqueous-based fire retardant composition and drying the wetted fabric while maintaining it in its stretched state.
Another example of a nonwoven fabric having comparable strength in the machine and cross directions is illustrated by U.S. Pat. No. 5,296,289, issued to Collins on Mar. 22, 1994. Collins discloses a spun bonded nonwoven web having spaced autogenous spot bonds, wherein spot bonds are distributed in a cornrow pattern to form a web having improved strength.
Conventionally formed high loft nonwoven fabrics have limited use since their tensile strength in the machine direction is significantly less than that in cross direction. Moreover, improvement is also desired in other measures of product quality, such as fiber uniformity, resiliency, compression recovery, and reduction in false loft.
Conventional processes for forming high loft nonwoven fabrics also have process components that limit production rate well below that of the remaining equipment. The cross lapper typically limits the rate of production in that it is incapable of obtaining the production speeds of the remaining equipment.
Conventional processes that spray resin as a binder onto the web have a production rate much slower than those that utilize low melt fibers because the step of applying resin causes a process restriction point. Also the oven cure residence time to dry and cure the sprayed binder resin impedes the production process compared with using low melt fibers. Using low melt fibers, on the other hand, is often more expensive than spraying a binder resin.